Cathode-ray device



Sw ft. 3; 1946. R... P. JOHNSON ErAL GATHODE RAY DEVICE Filed Jan. 27, .1943

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RWW

Thei Attorney.

Patented Sept. 3, 1946 RalphP. Johnson and WilliamR. Grams, Sche-- nectady, N. Y. assignors: to General Electric Company, a corporation of New York Application January 27, 1943, Serial No. 473,706

4, Claims.

The present invention relates to cathode ray devices of the. type. known as. dark trace tubes:

(for skiatrons) wherein a dark pattern is. produced on a screen of suitable material by the impingement. thereon of a beam of electrons. It. is. the aim of our invention to improve; the optical eiliciency of. such devices.

The pattern on thescreen of. a dark tracetube. may be viewed by light which falls. on the screen. from an external source andis diffusely reflected. therefrom to the eye of the observer- The pattern on a dark trace screen also may be projected by optical means, including a mirror or lens arranged to form an enlarged image, the light. employed for such projection being incident on the screen. from an external. source. In the past it has. been customary to provide on the interior surface of the. envelope of cathode ray tubes. an electrically conducting layer, for example, a graphite layer. Such layers also were light-absorbing.

In consequence. of our invention the efiectiveness; of darktrace cathode ray deviceshas been improved by providing on the interior or exterior surface of a portion of. theenvelope a. matte white surface. A large. fraction of the imping-- ing light penetrating through the screen. is. diffusely reflected. from this matte white surface and is returned. through the screen to the optical system employed for. projecting the image, or reaches the observer direct with accompanying advantages as will be explained. In a. preferred embodiment. of our invention a metallic. reflecting; foundation coating. first is produced on. the

interior glass surfaceof the envelope; Upon this reflecting foundation. a layer of matte white. material is deposited. I

Fig. L of the accompanying drawing is a. side. view of a cathode ray device, shown partly broken away, and. embodying a preferred form of. our invention; Fig. 2 is a front view; Fig. 3 illustrates a. modification; and Fig. 4 is a diagrammatic view of one form of an optical projection system em bodying a dark trace cathode ray device.

Theenvelope of the cathode ray tube of Fig. 1, which may consist of glass or other transparent material, is elongated and includes an end chamher 5 which is of greater diameter than the adjoining elongated tubular portion 6. Within the tubular portion 6 adjacent the opposite end (broken away in the drawing) is located a socalled electron gun 8, whereby a beam of electrons is projected upon a screen which is deposited on the interior surface of the window 1. The construction and operation of such electron guns I 2.. and associated. means for focusing and deflect.- ing the electron beam are. well known to those skilled; in. the art.v The chamber 5 is closed at. one endv by a relatively thick. screen-carrying; wall 1;- which may be flat, or: may have. a. moderateconvex curvature toincrease its resistance to citternal airpressure.

Before. the parts ofthe device are assembled, the interior surface of the tubular part. 6 of. the envelopeis coated with a layer 9 of graphite, orother suitable conducting, medium. This layer or: coating 9 may. be applied upon the interior surface; of the tubular part of the envelope be.- fore the end closures are. applied. The method described in United StatesLetters Patent. 21,264,- 358", issued. to Record, utilizing an: aqueous suspension of: graphite admixed withya dis.- persi'ng: agent, such. as, bentonite, is; suitable for this purpose. The coating; preferably; is baked in contact with the The cathode I4 of the electron. gun 8 is connected. to a. negative, terminal. of. a high voltage source 153 byagroundedconducton IS. The cathode is provided with a. filamentary heater and ordinarily, is coatedexternally with. alkaline, earth oxideto promote; electron emissivity.

Electrically in contact with the conducting:

coating-ll and extending; tothe. sealed-in terminal I illiiszaninternal. coating; l I of aluminum, orother suitable reflecting. metal. This coating constitutesa the so-called final anode in the device. It is connected. through the sealed-in lead l0 and a. conductor l2 to, thepositive terminal of the high.

voltagesource l3. Superimposed onthereflecting layer M is a layer of matte white material It; which. extends almost to the front wall. I of the. envelope...

In the fabrication. of the device. before. the front wall. 1 is applied, aluminum or other; re.- flectingi metal chosen to form the layer IL, is vaporized in any suitable way, as by high frequency induction heating or by passage of current. through a wire of. refractory metal (not. shown) on which a. pellet of. the metal to be vaporized has been placed.

A suitable gas-free, heat-resisting white. material, for example magnesium oxide, next is deposited on the inner surface of the side wall of the cathode ray tube as the indicated layer l6, Fig. 1. In accordance with one method, metallic magnesium may be burned in air and the resulting fumes or smoke conducted into contact with the surface to be coated. Deposition may also occur from a suspension of finely divided magnesium oxide in water. The suspension or slip is suitably applied and the resulting adherent layer is baked at about 400 C. in air. A getter material, for example barium or magnesium, may be introduced for the absorption of residual deleten'ous gas in the tube. A spring-supported getter metal, which can be vaporized by high frequency heating and deposited on the inner surface of the neck 6, is illustrated at IT.

Small masses of suitable screen material, for example potassium chloride, bromide, sodium chloride 01' other suitable halide of an alkali metal, are introduced in such Way that they are I is vaporized.

The face plate I is fusion-sealed to the rim of the main envelope 5 in any suitable way, for example by the combined effect of combustion heating and electrical high frequency heating, as described in United States Letters Patent 2,306,054 issued to Guyer. The electron gun 8 is sealed into place and the envelope is exhausted and baked to free the walls and enclosed metal parts of deleterious gases, all by well-known technique. The screen material next is deposited on the glass foundation, for example by high frequency heating of the cups [8 which contain the massive material. It is sublimed and deposits as a thin layer on the inner wall of the face plate 1. The cathode is activated and the other well-known fabrication steps are taken as usual. The perforated electrode or control grid 2| of the electron gun is connected by the conductor 22 to a point of potential on the source I3 which is negative with respect to the cathode l4. The electrode 23 also is connected to the source l3 by a conductor 24, as shown.

In another form of our invention, as shown in Fig. 3, the inner wall of the envelope 5 is left bare except for a narrow strip 25-of a suitable conducting material, such as graphite, which connects the coating 9 to the sealed-in lead l0. After fabrication of the device according to the method outlined above herein, a coat 26 of suitable white material, such as an enamel or paint, is applied upon the exterior of the side wall of the envelope 5. To-increase the diffuseness of reflection from the wall of the cathode ray tube, its inner surface may be roughened in any suitable fashion, such as by sandblasting, before the device is assembled.

The advantages of our invention in increasing the brightness and visibility of a pattern formed on the screen by electron impact appear when our improved'devices are viewed directly or are employed in' an optical projection system such as the Schmidt projector shown in Fig. 4. As shown here, the pattern on the screen of the cathode ray device 30 is illuminated by a projection lamp which is diagrammatically indicated at 3|. Light from the screen thus illuminated falls on the concave mirror 32 from which it. is projected on a Heat is applied 7 (as by high frequency induction) until the halide distant surface, diagrammatically indicated at 33 through a correcting lens 34 gripped on its periphery by a holder 35. If the cathode my device 30 is one which employs our invention, a large fraction of the light which proceeds through the screen of the device and strikes the wall of the envelope is returned in a forward direction, that is, through the screen into the concave mirror and thence to the final image, increasing its brightness and visibility.

We do not wish to limit ourselves to the particular optical projection system shown in Fig. 4, nor to the details of construction of the described cathode ray devices. We have described some of these details, which are not a part of the present invention, in order to make clear the nature of our invention and how it is to be performed. It will be evident to those skilled in the art that other details of construction of the cathode ray device can be chosen, and other forms of optical apparatus can be used for viewing the screen or for projecting the pattern appearing thereon, without departing from the spirit and scope of the present invention.

What we claim as new and desire to secure by Letters Patent of the United States is:

1, A cathode ray devicelcomprising a tubular envelope, a dark trace screen therein, means for producing a pattern on said screen and a matte white reflector adjacent said screen in such position that said reflector will constitute a lightdiifusing background for a pattern on said said screen.

2. An electron discharge device comprising an elongated envelope, a dark trace screen located at one end of said device, cooperating electrodes in said device remote from said screen whereby electrons may be projected on said screen, and a coating of white material on a side wall surface of said envelope adjacent said screen, to increase the visibility of a dark screen pattern when illuminated by light projected thereon.

3. A cathode ray device comprising an elongated envelope having a cathode-ray-responsive screen at one end thereof, means longitudinally displaced in said envelope for projecting a beam of electrons on said screen, means for deflecting said beam in response to external impulses, a coating of light-reflecting material on the inner surface of said envelope adjacent said screen, and a coating of light-diffusing material superimposed on said reflecting material.

4. An electron discharge device comprising an elongated envelope, ascreen of alkali halide lo cated at one end of said device, an electrode constituted of an electrically conductive coating on the inner surface of said envelopeadjacent said screen, cooperating electrodes in said device remote from said screen whereby electrons may be projected on said screen, and a coating of magnesium oxide on said conductive coating on an interior surface of said envelope adjacent said screen.

RALPH P. JOHNSON. WILLIAM R. GRAMS. 

